The precocious winger has denied claims he felt snubbed by coach Marcelo Bielsa in recent weeks, and has vowed his performances will improve in line with his fitness
Athletic have flattered to deceive this year, playing poorly and sitting in a disappointing 14th place in La Liga.
Munian, who was a revelation at home and in the Europa League last season, has been particularly underwhelming this campaign, but is adamant he can improve if he maintains his fitness.
“My drop in form is due to a bit of everything, but the main thing is that I was not fully fit," the 20-year-old told reporters.
“[Fitness] is critical to my game and at times it has influenced things. However, the Betis game showed that I am recovering and am much better than in previous games."
Despite an improved performance, Munian was withdrawn early by Bielsa, prompting a perceived show of dissent.
“Was I angry at being replaced in that game? I was doing well, but obviously I have to respect the coach’s decision," Muniain said.
“I was angry with myself because every player likes to play every minute. When I don’t get angry for leaving the field, that is when you should worry."